The present invention relates to a motor control circuit, and specifically to a control circuit for controlling a DC brushless motor which drives the cylinder of a helical scan video tape recorder.
In conventional video tape recorders of the helical scan type, magnetic tape is wound on a rotary cylinder having a pair of video heads so that the tape is obliquely scanned by the heads. The cylinder is driven by a multi-phase DC brushless Ws motor having Hall generators which detect the relative position of the rotor for switching the current supplied to stator coils. The Hall generators are associated respectively with the stator coils. To permit the video heads to precisely trace the intended tracks it is necessary that the rotational speed and angle of the cylinder be controlled to within the specified range of close tolerances. Currently, a tachogenerator is employed to detect the speed of the cylinder and the rotational angle of the cylinder is derived by a proximity sensor which detects the proximity to rotating magnets mounted in diamterically opposite positions of the cylinder. It has therefrom been desired to reduce the components and simplify the motor control circuitry.